Remove the need to specify the full harness path

Instead -Iharness-name can be used

Author: luke-gruber

harness/loader.rb

@@ -1,4 +1,13 @@
 # Use harness/harness.rb by default. You can change it with -I option.
 # i.e. ruby -Iharness benchmarks/railsbench/benchmark.rb
-$LOAD_PATH << File.expand_path(__dir__)
-require "harness"
+retries = 0
+begin
+  require "harness"
+rescue LoadError => e
+  if retries == 0 && e.path == "harness"
+    retries += 1
+    $LOAD_PATH << File.expand_path(__dir__)
+    retry
+  end
+  raise
+end